/*
 *    Copyright 2009-2012 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.io;

import java.io.IOException;
import java.lang.annotation.Annotation;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.apache.commons.lang.StringUtils;
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.logging.LogFactory;

/**
 * <p>
 * ResolverUtil is used to locate classes that are available in the/a class path
 * and meet arbitrary conditions. The two most common conditions are that a
 * class implements/extends another class, or that is it annotated with a
 * specific annotation. However, through the use of the {@link Test} class it is
 * possible to search using arbitrary conditions.
 * </p>
 * <p/>
 * <p>
 * A ClassLoader is used to locate all locations (directories and jar files) in
 * the class path that contain classes within certain packages, and then to load
 * those classes and check them. By default the ClassLoader returned by
 * {@code Thread.currentThread().getContextClassLoader()} is used, but this can
 * be overridden by calling {@link #setClassLoader(ClassLoader)} prior to
 * invoking any of the {@code find()} methods.
 * </p>
 * <p/>
 * <p>
 * General searches are initiated by calling the
 * {@link #find(org.apache.ibatis.io.ResolverUtil.Test, String)} ()} method and
 * supplying a package name and a Test instance. This will cause the named
 * package <b>and all sub-packages</b> to be scanned for classes that meet the
 * test. There are also utility methods for the common use cases of scanning
 * multiple packages for extensions of particular classes, or classes annotated
 * with a specific annotation.
 * </p>
 * <p/>
 * <p>
 * The standard usage pattern for the ResolverUtil class is as follows:
 * </p>
 * <p/>
 * 
 * <pre>
 * ResolverUtil&lt;ActionBean&gt; resolver = new ResolverUtil&lt;ActionBean&gt;();
 * resolver.findImplementation(
 * 		ActionBean.class, pkg1, pkg2);
 * resolver.find(new CustomTest(), pkg1);
 * resolver.find(new CustomTest(), pkg2);
 * Collection&lt;ActionBean&gt; beans = resolver
 * 		.getClasses();
 * </pre>
 * 
 * @author Tim Fennell
 */
public class ResolverUtil<T> {
	/*
	 * An instance of Log to use for logging in this class.
	 */
	private static final Log log = LogFactory
			.getLog(ResolverUtil.class);

	/**
	 * A simple interface that specifies how to test classes to determine if
	 * they are to be included in the results produced by the ResolverUtil.
	 */
	public static interface Test {
		/**
		 * Will be called repeatedly with candidate classes. Must return True if
		 * a class is to be included in the results, false otherwise.
		 */
		boolean matches(Class<?> type);
	}

	/**
	 * A Test that checks to see if each class is assignable to the provided
	 * class. Note that this test will match the parent type itself if it is
	 * presented for matching.
	 */
	public static class IsA implements
			Test {
		private Class<?> parent;

		/**
		 * Constructs an IsA test using the supplied Class as the parent
		 * class/interface.
		 */
		public IsA(Class<?> parentType) {
			this.parent = parentType;
		}

		/**
		 * Returns true if type is assignable to the parent type supplied in the
		 * constructor.
		 */
		public boolean matches(
				Class<?> type) {
			return type != null
					&& parent
							.isAssignableFrom(type);
		}

		@Override
		public String toString() {
			return "is assignable to "
					+ parent.getSimpleName();
		}
	}

	/**
	 * A Test that checks to see if each class is annotated with a specific
	 * annotation. If it is, then the test returns true, otherwise false.
	 */
	public static class AnnotatedWith
			implements Test {
		private Class<? extends Annotation> annotation;

		/** Constructs an AnnotatedWith test for the specified annotation type. */
		public AnnotatedWith(
				Class<? extends Annotation> annotation) {
			this.annotation = annotation;
		}

		/**
		 * Returns true if the type is annotated with the class provided to the
		 * constructor.
		 */
		public boolean matches(
				Class<?> type) {
			return type != null
					&& type.isAnnotationPresent(annotation);
		}

		@Override
		public String toString() {
			return "annotated with @"
					+ annotation
							.getSimpleName();
		}
	}

	/** The set of matches being accumulated. */
	private Set<Class<? extends T>> matches = new HashSet<Class<? extends T>>();

	/**
	 * The ClassLoader to use when looking for classes. If null then the
	 * ClassLoader returned by Thread.currentThread().getContextClassLoader()
	 * will be used.
	 */
	private ClassLoader classloader;

	/**
	 * Provides access to the classes discovered so far. If no calls have been
	 * made to any of the {@code find()} methods, this set will be empty.
	 * 
	 * @return the set of classes that have been discovered.
	 */
	public Set<Class<? extends T>> getClasses() {
		return matches;
	}

	/**
	 * Returns the classloader that will be used for scanning for classes. If no
	 * explicit ClassLoader has been set by the calling, the context class
	 * loader will be used.
	 * 
	 * @return the ClassLoader that will be used to scan for classes
	 */
	public ClassLoader getClassLoader() {
		return classloader == null ? Thread
				.currentThread()
				.getContextClassLoader()
				: classloader;
	}

	/**
	 * Sets an explicit ClassLoader that should be used when scanning for
	 * classes. If none is set then the context classloader will be used.
	 * 
	 * @param classloader
	 *            a ClassLoader to use when scanning for classes
	 */
	public void setClassLoader(
			ClassLoader classloader) {
		this.classloader = classloader;
	}

	/**
	 * Attempts to discover classes that are assignable to the type provided. In
	 * the case that an interface is provided this method will collect
	 * implementations. In the case of a non-interface class, subclasses will be
	 * collected. Accumulated classes can be accessed by calling
	 * {@link #getClasses()}.
	 * 
	 * @param parent
	 *            the class of interface to find subclasses or implementations
	 *            of
	 * @param packageNames
	 *            one or more package names to scan (including subpackages) for
	 *            classes
	 */
	public ResolverUtil<T> findImplementations(
			Class<?> parent,
			String... packageNames) {
		if (packageNames == null)
			return this;

		Test test = new IsA(parent);
		for (String pkg : packageNames) {
			find(test, pkg);
		}

		return this;
	}

	/**
	 * Attempts to discover classes that are annotated with the annotation.
	 * Accumulated classes can be accessed by calling {@link #getClasses()}.
	 * 
	 * @param annotation
	 *            the annotation that should be present on matching classes
	 * @param packageNames
	 *            one or more package names to scan (including subpackages) for
	 *            classes
	 */
	public ResolverUtil<T> findAnnotated(
			Class<? extends Annotation> annotation,
			String... packageNames) {
		if (packageNames == null)
			return this;

		Test test = new AnnotatedWith(
				annotation);
		for (String pkg : packageNames) {
			find(test, pkg);
		}

		return this;
	}

	/**
	 * Scans for classes starting at the package provided and descending into
	 * subpackages. Each class is offered up to the Test as it is discovered,
	 * and if the Test returns true the class is retained. Accumulated classes
	 * can be fetched by calling {@link #getClasses()}.
	 * 
	 * @param test
	 *            an instance of {@link Test} that will be used to filter
	 *            classes
	 * @param packageName
	 *            the name of the package from which to start scanning for
	 *            classes, e.g. {@code net.sourceforge.stripes}
	 */
	public ResolverUtil<T> find(
			Test test,
			String packageName) {
		String path = getPackagePath(packageName);

		try {
			List<String> children = VFS
					.getInstance()
					.list(path);
			for (String child : children) {
				if (child
						.endsWith(".class"))
					addIfMatching(test,
							child);
			}
		} catch (IOException ioe) {
			log.error(
					"Could not read package: "
							+ packageName,
					ioe);
		}

		return this;
	}

	/**
	 * Converts a Java package name to a path that can be looked up with a call
	 * to {@link ClassLoader#getResources(String)}.
	 * 
	 * @param packageName
	 *            The Java package name to convert to a path
	 */
	protected String getPackagePath(
			String packageName) {
		return packageName == null ? null
				: packageName.replace(
						'.', '/');
	}

	/**
	 * Add the class designated by the fully qualified class name provided to
	 * the set of resolved classes if and only if it is approved by the Test
	 * supplied.
	 * 
	 * @param test
	 *            the test used to determine if the class matches
	 * @param fqn
	 *            the fully qualified name of a class
	 */
	@SuppressWarnings("unchecked")
	protected void addIfMatching(
			Test test, String fqn) {
		try {
			String externalName = fqn
					.substring(
							0,
							fqn.indexOf('.'))
					.replace('/', '.');
			ClassLoader loader = getClassLoader();
			log.debug("Checking to see if class "
					+ externalName
					+ " matches criteria ["
					+ test + "]");

			Class<?> type = loader
					.loadClass(externalName);
			if (test.matches(type)) {
				matches.add((Class<T>) type);
			}
		} catch (Throwable t) {
			log.warn("Could not examine class '"
					+ fqn
					+ "'"
					+ " due to a "
					+ t.getClass()
							.getName()
					+ " with message: "
					+ t.getMessage());
		}
	}

	public static String trimComma(
			String para) {
		if (StringUtils
				.isNotBlank(para)) {
			if (para.endsWith(",")) {
				return para
						.substring(
								0,
								para.length() - 1);
			} else {
				return para;
			}
		} else {
			return "";
		}
	}
}